With recent advances in computerization, the need for equipment for storing information, especially small-size and large capacity recording devices, has continued to increase. To respond to these needs, technology for improving the recording density per unit area of magnetic recording media have intensively been developed by various research facilities.
To increase the recording density, it has been required to develop a medium having a high coercive force capable of allowing an infinitesimal magnetic domains written in the recording medium of the medium to coexist stably, a recording head capable of writing the infinitesimal magnetic domain in the medium, and a read head capable of detecting a leakage magnetic field from the infinitesimal magnetic domain.
A conventional magnetic head has been composed of an element having both functions of recording and reproduction. With the reduction of the diameter of the medium due to the size reduction of the device, the linear velocity in the direction of magnetization reversal decreases. Therefore, it has become standard to install a read head comprising a magnetoresistive (MR) element utilizing the magnetoresistive effect capable of stably detecting the leakage magnetic field with high sensitivity without depending on the linear velocity. Namely, current magnetic heads are composed of a combination of a write-only recording head and a read-only read head.
As is apparent from such a technical trends, a high magnetic pole material having a high saturation magnetic flux density, capable of generating a strong magnetic field will be essential to next generation recording heads in order to sufficiently magnetize a medium having a high coercive force, to thereby record a signal.
As the magnetic pole material which has preferably been used heretofore, for example, a permalloy (78 wt % Ni—Fe alloy) having a saturation magnetic flux density of about 1 tesla (T) is well known. Further, sendust (Fe—Al—Si alloy) having a saturation magnetic flux density of about 1.1-1.2 T and a Co-based amorphous material having a saturation magnetic flux density of about 1.5 T have been developed as materials having an improved saturation magnetic flux density.
The following materials have attracted special interest recently.
(1) Japanese Patent Application, First Application No. Hei 11-074122 (referred to as publication 1) discloses a method of producing a Co—Fe—Ni alloy film using a plating method. It describes that it is possible to produce a Co—Fe—Ni alloy having a crystal structure comprising a α′ phase having a body-centered cubic structure and an τ phase having a face-centered cubic structure wherein the cobalt content is within a range from 40 to 70% by weight, the iron content is within a range from 20 to 40% by weight, and the nickel content is within a range from 10 to 20% by weight and that the resulting alloy film has a small coercive force, small magnetostriction and saturation magnetic flux density of 2 T or more. It also describes that a post heat treatment at 100° C. or higher is effective to improve the corrosion resistance.
(2) Japanese Patent Application, First Application No. Hei 08-107036 (referred to as publication 2) discloses a method of producing an alloy film consisting essentially of Fe or Co using a sputtering method. It describes, as a material of a magnetic film which exhibits soft magnetic characteristics by a heat treatment, a material consisting of an alloy comprising Fe or Co as a principal element, at least one element selected from Ta, Zr, Hf and Nb in a concentration within a range from 5 to 20 atomic % and at least one element selected from Si, B, C and N in a concentration within a range from 5 to 20 atomic %, said material further comprising at least one element other than the magnetic element, which is selected from Al, Ti, Cr, Ru, Rh, Pt, Pd, Mo and W in a concentration within a range from 1 to 20 atomic %. The resulting alloy film has a saturation magnetic flux density of 1.5 T, a coercive force of 0.1 Oe (1 Oe=about 79 Å/m), a permeability of 3000 or more and magnetostriction constants of 10−7 level, and also has good soft magnetic characteristics.
(3) SUGITA et al. about a method of producing single crystal Fe16N2 film using a MBE (molecular beam epitaxy) method as follows [Y. SUGITA et al., J. Appl. Phys. 76, 6637 (1994), referred to as publication 3]. As a substrate, a special substrate of In00.2Ga00.8As (001) wherein the length of the a-axisnd lattice constants of a Fe16N2 film to be formed are nearly allowed to agree with each other is used. First, this substrate is heat-treated (675° C., five minutes) in a vacuum and then iron as a deposition source is scattered in a nitrogen atmosphere by means of an electron beam to form an iron nitride film containing about 11 atomic % of nitrogen. In that case, it is important to control a film deposition rate within a range from 0.002 to 0.003 nm/sec and to control a gas pressure within a range from 0.1 to 0.2 mTorr during the formation of a film. The resulting iron nitride film was a martensite (a) film and the saturation magnetic flux density thereof was about 2.4 T. After film formation, the film was subjected to a heat treatment at 200° C. in a vacuum on the order of 10−8 Torr, i.e. an annealing treatment for 90 hours to obtain a single crystal Fe16N2 (α′) film having a saturation magnetic flux density of about 2.9 T.
However, the prior arts described above had the following problems.
{circle around (1)} According to the technology disclosed in the publication 1, a magnetic pole material of a recording head is produced by a wet process such as a plating method. On the other hand, it is difficult to produce a MR element which also constitutes a read head by the plating method and the MR element must be produced by a dry process such as a sputtering method. Accordingly, the production of the magnetic pole material by means of the plating method should be avoided from the viewpoint that a cheap production process is constructed by avoiding double investment or an interfacial control relating to two processes (e.g. avoidance of contamination, retention of evenness, etc.) is stabilized.
{circle around (2)} In the technology disclosed in the publication 1, it is necessary to form a primary plating layer on an insulating layer by a sputtering method for a plating layer made of the above material constituting a magnetic pole. This step is indispensable for the magnetic pole material of the publication 1 to satisfy the desired characteristics. However, it is merely the addition of a useless section or a useless interface in view of the head structure and, therefore, it can promote peeling of a film and striction, which are caused by the interface.
{circle around (3)} It can be judged to be indispensable to add a post heat treatment at 100° C. or higher or a protective film because of poor corrosion resistance of the magnetic pole material of the publication 1 after film formation. This fact suggests that a countermeasure must be considered when the magnetic pole material of the publication 1 is applied to a product.
{circle around (4)} Since the magnetic pole material of the publication 2 is capable of producing a recording head by the same sputtering method as that used in case of the MR element constituting the read head, the material can be highly rated for promote production of all magnetic heads by means of the dry process. However, it must be said that the resulting saturation magnetic flux density of about 1.5 T is not enough to write information in a medium having a coercive force of 2500 oersted or more, which is used to increase the recording density.
{circle around (5)} The magnetic pole material of the publication 2 must be at least a quarternary material and a quinary material is described in the embodiments. As a result, the margin of the composition ratio capable of attaining a good saturation magnetic flux density is likely to be narrow and accurate control of the composition of the film is required.
{circle around (6)} It is necessary for the magnetic pole material of the publication 2 to control the grain size in order to obtain the desired magnetic characteristics, and a heat treatment is indispensable to obtain the desired magnetic characteristics after film formation. For example, it is described that the formed film is heat-treated at 490° C., which is 50° C. lower than the crystallization temperature, for three hours and then heat-treated at 590° C. for 30 minutes. In the case that a recording head is formed after forming a read head, this heat treatment is a process which cannot be employed because it can cause turbulence at the interface of an MR element composed of a laminate of very thin layers, which constitute the read head, resulting in deterioration of the characteristics of the MR element.
{circle around (7)} The magnetic film of the publication 3 has the feature that the highest saturation magnetic flux density, 2.9 T among all the saturation magnetic reflux densities that have ever been reported, and can be formed by a MBE method a dry processes. However, it had never been applied to an actual process of producing a magnetic head because a magnetic film having the desired characteristics cannot be obtained only on the surface of a special substrate and the film deposition rate is very small, such as 0.002-0.003 nm/sec and is not suited for use in the mass-production processes.
For the reasons described above, it has been desired to develop a magnetic pole material for a recording head which simultaneously satisfies the following conditions, and a method of producing the same in the production process of a recording/reproduction separated type magnetic head.
(A) A magnetic pole material having a saturation magnetic flux density of 1.5 T or more, preferably 2 T or more.
(B) A magnetic pole material having a coercive force of 2 Oe or less, preferably 1 Oe or less.
(C) A magnetic pole material which can be produced by the same dry process as that used in the production of a MR element of a read head, and a method of production the same.
(D) A method having a film deposition rate suited for use in the mass-production processes, i.e. applicability to a production process capable of using a cheap production line.
(E) A magnetic pole material which can be formed at a low temperature of not higher than 100° C. so as not to exert an effect on an interface of a thin film laminate produced previously, e.g. MR element, and a method of producing the same.
It has been reported that these plural conditions can be satisfied, for example, in the report of KIM and TAKAHASHI Issued in 1972 [T. K. KIM and M. TAKAHASHI, Appl. Phys. Lett. 20, 492 (1972) ].
In this report, it deserves special mention that an iron nitride film having a low coercive force and a very high saturation magnetic flux density of 2.58 T was formed on a substrate maintained at about room temperature at a mass-producible film deposition rate by using a very simple thin film forming method such as a deposition method, as once dry process. Although additional tests were conducted in various research facilities, a stable magnetic film having the characteristics described above could not be obtained and was formed only under the special conditions as described in the publication 3.
Accordingly, now, a magnetic pole material for a recording head which satisfies the conditions described in (A) to (E), and a method of producing the same, are strongly required.
Although the description above dealt particularly with a magnetic head for longitudinal magnetic recording, a magnetic pole material having the above characteristics, i.e. “saturation magnetic flux density of 1.5 T or more, preferably 2 T or more” and “coercive force of 2 Oe or less, preferably 1 Oe or less can also be employed as a magnetic pole material constituting a magnetic head for perpendicular magnetic recording, as a matter of course. Accordingly, the magnetic material having the above saturation magnetic flux density can also be employed as a magnetic head for perpendicular magnetic recording. Therefore, it has been required to develop such a magnetic thin film having excellent soft a magnetic characteristics because it can be employed widely in the field of the magnetic recording for either longitudinal or perpendicular recording.
It has been desired to employ a magnetic thin film, which satisfies the conditions described in (A) to (E) and a method of producing the same, as various magnetic head devices described below, in addition to application to the magnetic pole material constituting the magnetic head.
(AL1) A magnetic thin film to be formed on a hard magnetic film which serves as a recording layer constituting a longitudinal magnetic recording medium.
(AL2) A magnetic thin film to be formed under a hard magnetic film which serves as a recording layer constituting a perpendicular magnetic recording medium.
(AL3) A magnetic thin film to be used as at least portion of a soft magnetic film constituting an exchange-spring magnet or a spin transistor magnet.
(AL4) A magnetic thin film to be used as at least portion of a transition line constituting a magnetic sensor.
(AL5) A magnetic thin film to be used as at least portion of a transition line constituting a high frequency passive device.
(AL6) A magnetic thin film to be used as at least portion of a transition line constituting a micro transformer or a micro inductor.
Also in any of magnetic devices described in (AL1) to (AL6), it is possible to expect that the magnetic pole material having the above characteristics, i.e. “saturation magnetic flux density of 1.5 T or more, preferably 2 T′ or more” and “coercive force of 2 Oe or less, preferably 1 Oe or less” can further improve various characteristics of various magnetic devices.
The first object of the present invention is to provide a magnetic thin film having soft magnetic characteristics with at least a saturation magnetic flux density of 2 T or more and a coercive force of 2 Oe or less without requiring any heat treatment during and after forming a film.
The second object of the present invention is to provide a method of producing a magnetic thin film having soft magnetic characteristics suited for use as a magnetic pole material of a recording head, which can be produced by the same dry process as that in case of a MR element constituting a read head.
The third object of the present invention is to provide a method of evaluating, which comprises specifying that a film during or after forming the film is an iron carbide film comprising an α′ phase as a principal phase and at least carbon and iron as a constituent element.
The fourth and fifth objects of the present invention are to provide a magnetic head capable of recording a signal by sufficiently magnetizing a medium having a high coercive force, and a magnetic recording device equipped with the same.
The sixth object of the present invention is to provide a magnetic recording medium capable of coping with an increase of the recording density.
The seventh object of the present invention is to provide various magnetic devices having various excellent characteristics as compared with the prior art, e.g. excellent characteristics in energy product, frequency, and current density.